This invention relates to anaerobically-curing compositions.
Anaerobically-curing compositions generally comprise polymerizable acrylate monomers and free-radical initiators. When maintained in an oxygen-containing environment, such compositions remain uncured (i.e., unpolymerized). However, in the absence of oxygen, such as when an anaerobically-curing composition is placed between surfaces which are in close engagement with one another (e.g. a nut and bolt), cure will ensue.
Anaerobically-curing compositions containing peroxy initiators (e.g., peroxides and hydroperoxides) or inorganic salt initiators (e.g., persulfates or perchlorates of ammonium, an alkali metal or an alkaline earth metal) are well-known in the art, having been described, for example, in U.S. Pat. Nos. 2,895,950 (Krieble) and 4,090,997 (Patel et al.) respectively. Commonly such compositions contain quinone-type compounds which act as polymerization inhibitors, thereby maintaining the compositions in an uncured state when stored in the presence of oxygen. Such compositions may also contain an organic sulfimide and/or an amine as an accelerator.
Unfortunately, anaerobically-curing compositions which contain peroxy initiators or inorganic salt initiators may possess certain disadvantages. For example, there is often the possibility of explosion whenever large amounts of peroxy compounds or inorganic salt initiators are handled, such as during manufacture of these compositions. Furthermore, unfortunately, peroxy compounds and inorganic salt initiators often decompose with time, thus resulting in a steadily decreasing ability of such compounds to initiate the polymerization of compositions containing them.
While one-part anaerobically-curing compositions containing polymerization initiators other than peroxy initiators or inorganic salt initiators are known in the art, such compositions may fail to exhibit a suitable balance of shelf-life stability versus cure-rate. In particular, while such compositions may exhibit suitable shelf-life stability in the presence of oxygen, they may cure at unsatisfactory rates when oxygen is excluded. Alternatively, such compositions often cure rapidly in the absence of oxygen, but may exhibit unsatisfactory shelf-lives.
The combination of saccharin and certain aromatic amines is known to be extremely effective in initiating rapid anaerobic cure of acrylate-containing compositions without the presence of additional peroxy or organic salt initiators. However, a one-part composition containing saccharin and an amine as the initiator combination generally will exhibit a less than suitable shelf-life unless a substantial amount of a quinone or hydroquinone polymerization inhibitor is added which unfortunately also results in a very slow rate of cure of the composition. Thus, two-part compositions, with one part containing the saccharin and the other part containing the amine, generally have been employed when it is desired to use that particular initiator combination, e.g., U.S. Pat. No. 3,658,624 (Lees).
One example of a one-part, anaerobically-curing composition containing saccharin and an amine as the initiator combination is described in Japanese Patent application No. JA 51-119050. Unfortunately, suitable shelf-life stability of that composition is only obtained when certain monomers such as trimethylol-propane trimethacrylate are employed as the polymerizable monomer. Since most commonly available monomers are unsuitable for employment in that composition, the composition is greatly limited in terms of practicality.
Thus, in view of the foregoing, it would be desirable to have a polymerization inhibitor which would permit employment of the particularly effective initiator combination of saccharin and an amine in one-part, anaerobically-curing compositions. A suitable polymerization inhibitor should impart suitable shelf-life stability to the composition and will, at the same time, not hinder free-radical initiated polymerization which ensues in the absence of oxygen on an active metal surface.
N-nitrosamines have been employed as antioxidants in the manufacture of rubber-containing articles, as additives in persulfate or perchlorate-containing anaerobically-curing sealants to limit corrosion of metallic substrates, e.g. U.S. Pat. Nos. 4,090,997 and 4,166,169 (both to Patel et al.), and as polymerization accelerators in dental resins, e.g. U.S. Pat. No. 2,558,139 (Knock). However, it has not heretobefore been proposed to use N-nitrosamines as polymerization inhibitors in anaerobically-curing compositions comprising an organic sulfimide and an amine as the initiator components.